<!doctype html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
</head>
<style>
		.a{
			width:0px;
			height:0px;
			border-style:solid;
			border-width:50px;
			border-top-width:0px;
			border-color:green transparent;
			margin:auto;
		}
		.b{
			border-width:100px;
			border-top-width:0px;
		}
		.c{
			border-width:200px;
			border-top-width:0px;
		}
		.d{
			border-width:300px;
			border-top-width:0px;
		}

</style>
<body>
	<div class="a "></div>
	<div class="a b"></div>
	<div class="a c"></div>
	<div class="a d"></div>
</body>
</html>